DALLAS — In a rare reunion, the five living American presidents gathered in Dallas Thursday to honor one of their own at the dedication of the George W. Bush Presidential Center. The presidents — Bush, Barack Obama, Bill Clinton, George H.W. Bush and Jimmy Carter — were cheered by a crowd of former White House officials and world leaders as they took the stage together to open the dedication. They were joined on stage by their wives — the nation’s current and former first ladies — for the outdoor ceremony on a sun-splashed Texas morning. The leaders were putting aside the ideological differences that have divided them for years for a day of pomp and pleasantries. For Bush, 66, the ceremony also marked his unofficial return to the public eye four years after the end of his deeply polarizing presidency. Clinton jokes that he’s become so close to the Bushes that he’s become “the black sheep son.” During a speech at the dedication on the campus of Southern Methodist University, Clinton said Bush had a beautiful library and that his institute’s work was inspiring. Clinton also noted that Bush had beaten him to becoming a grandfather and joked with him about his newfound hobby of painting. Clinton and Carter both noted Bush’s humanitarian causes. Wearing dark sunglasses, Carter credited Bush for helping broker a peace treaty in Sudan after he took office. In a reminder of his duties as the current Oval Office inhabitant, Obama planned to travel to Waco in the afternoon for a memorial for victims of last week’s deadly fertilizer plant explosion.